1. Field of the Invention
The present invention relates to medical treatment of tumor tissue, and more specifically, deals with optimizing tissue destruction with focused ultrasound heating.
2. Description of Related Art
Devices have been developed which focus ultrasonic sound waves at a focal point deep within a subject. At the focal point, energy is dissipated and local heating results. Of the tissue is allowed to come to a sufficiently high temperature for a sufficiently long period of time, the tissue will be denatured and be re-absorbed by the body. In this manner, tumors can be killed as without the necessity of an operation.
In some cases, it may not be possible to locally heat a tumor to a high enough temperature without causing serious damage to the patient. For example, a tumor tangled around the brain stem may not be treatable by this method because of the danger of thermal damage to the brain stem.
Another method of destroying tumor tissue is through chemotherapy. In conventional chemotherapy, a patient is injected with a poisonous compound that concentrates in the faster growing tissue of a tumor. The dose of the poisonous compound is adjusted such that the concentration in the normal tissue does not reach toxic levels while the concentration in the tumor is high enough to destroy it.
One alterative to simple chemotherapy is photodynamic therapy where the body is injected with a photosensitive compound that tends to concentrate in the tumor. The primary photosensitive compound itself is harmless. However, when the compound is exposed to light, it breaks down into successor compounds at least one of which is toxic to the tissue. By concentrating light on the tumor, the compound break down and toxicity are limited to the tumor. One problem with this approach is that the patient is largely opaque and any light that is transmitted by the body is highly scattered and diffuse. Consequently, it is difficult to expose tumors in many parts of the body to light.
In many medical procedures, it is important to accumulate a certain chemical entity to a desired tissue type. In chemotherapy, it is important to deliver drugs to a cancerous tumor tissue. Traditional anti-tumor therapies, including chemotherapy and radiation treatments, rely upon a differential response between normal tissue and cancerous cells. However, there remains unavoidable toxicity towards normal tissue which causes substantial side effects and limit practical drug dosages.
Much work has been done in the area of developing specific chemical entities attached to antibodies, that are specific to tumor antigens. Delivery of chemical entities by this method is a difficult task since it requires finding antibodies which are specific to tumor antigens, and do not bind to other tissue. For most human tumors, the associated antibodies are not specific only to this type of tissue.
A further problem is that once antibody has been found that binds to the type of tumor intended to be destroyed, the delivery of the chemical entity may not be very large since the density of the antibodies on the surface of the cells of tumor tissue is generally not high.
Currently there is a need for a method of treatment of tumor tissue of a subject with limited collateral damage to adjacent tissues of the subject.